1. Field of the Invention
The present invention is concerned with a method and system for producing drawings generated by a computer aided design (CAD) system on an output image creation device such as a laser printer, imagesetter, or the like. More particularly, the present invention is concerned with identifying the drawing entities such as arcs, text, and the like and converting the plotting data in vector notation into corresponding plotting data in notation appropriate so that the image device can recreate images of curved lines as smooth curves and whereby the font style of the text can be selectively varied.
2. Description of the Prior Art
Computer aided design (CAD) systems greatly enhance the creation of engineering drawings, patent drawings, or the like both from the standpoint of initial drawing productivity and ease of corrections. Frequently, an X-Y pen plotter is used as the output image device from the CAD system for creating hard copy drawings. Although such drawings are adequate for many purposes, drawings produced by an X-Y pen plotter are often not print quality sufficient for subsequent offset lithographic processes.
In order to produce print quality drawings from CAD systems, various devices and methods have been devised which enable output to a raster-based print device such as electrostatic plotters, laser printers, dot matrix printers, and so forth. Such raster-based printers are desirable because they can produce print quality drawings having high resolution.
Various systems and methods are known in the prior art which convert drawing entity descriptions in vector format from a CAD system into raster-based descriptions suitable for input to a raster-based printer. For example, U.S. Pat. Nos. 4,254,467 and 4,458,330, which are hereby incorporated by reference, disclose systems and methods for converting entity descriptions in vector notation into raster formats suitable as input to raster-based image devices.
While such raster-to-vector conversion systems and methods have greatly enhanced the prior art, disadvantages still exist which inhibit the wider use of CAD systems. For example, a CAD system presents the output for a curve as a series of short, straight vectors. That is to say, even though the curved line segments such as an arc may be described mathematically as a smooth curve, the output from the CAD system describes the curve as short vectors which, in the limit, approximate a smooth curve. The vector-to-raster conversion systems and methods merely convert the short vectors into corresponding short line segments as the output image from the raster-based printer. Thus, the image of the curve on the finished drawing, while of print quality, is composed of a series of short, straight line segments.
Similarly, CAD systems present the output for text characters also as a series of straight vectors. Vector-to-raster converters in turn convert these vectors into a raster format for output as a corresponding plurality of straight line segments. The raster-to-vector converters are not designed to identify the text character as a character per se, and thus do not enable font style variation of the character.
Additionally, CAD systems even when used with vector-to-raster converters and raster-based printers, do not allow gray scale variation of the output drawing lines and, furthermore, do not provide the capability for reversing an image as white-on-black, for example, rather than the typical black-on-white image.